Measurements in the ultraviolet region of apparent absorption by barium sulfate sols

Absorbance measurements in the ultraviolet have been shown to be useful for following changes with time in the average particle size of barium sulfate sols. The effects of the method of adding the barium chloride, a change in the temperature, the presence of 1.00M calcium chloride and the percentage of ethanol in the solution have been examined as a function of time. By measuring the apparent absorbance of barium sulfate sols in 10 cm cells, sulfate can be determined in the range of 2.5–10.0 μg per ml. This is a range which, in the past, has had to be handled by nephelometry.